A central solar radiation receiver admits concentrated light at extremely high temperatures, commonly about 700.degree.-1500.degree. C., so that a solar absorber mounted therein, preferably a volumetric solar absorber, absorbs the incident concentrated light, converts it into heat and the so-generated heat is transferred to a heat carrier fluid, or is used to perform a thermochemical process.
Volumetric solar receivers generally have a tubular housing accommodating a volumetric solar absorber shielded by transparent window so as to form a sealed absorber chamber capable of holding a working fluid or a chemical reaction mixture in direct contact with the absorber. In operation, the working fluid or reaction mixture is caused to flow across the absorber chamber whereby heat is withdrawn from the absorber and is either utilized for the chemical reaction or is transported outside the receiver. Typical solar receivers with volumetric absorber are disclosed, for example, in U.S. Pat. No. 5,245,986 and U.S. Pat. No. 5,323,764.
The transparent window that shields the volumetric solar absorber in a solar receiver must be capable of sustaining the extreme conditions of high solar flux, high temperature and pressures associated with the conditions of operation. In recent patents such as U.S. Pat. No. 5,323,764, it was shown that conical windows that are placed inside the receiver to shield the absorber and form the sealed absorber chamber so that the axis of propagation of the solar light is along the axis of the conical window, perform extremely well under severe conditions of heat and pressure. Since the concentrated solar light is approaching the window at a wide angular distribution, it penetrates the window whenever it intersects therewith. The design of the window can be such that a small amount of light which is reflected in a single interaction between the light and the window will eventually penetrate the window after successive interactions.
For a solar receiver designed for use in large scale solar energy systems, large size transparent windows that meet the above requirements are required. However, windows with the necessary large dimensions and having the required optical qualities are not readily available. For example, the diameter of commercially available quartz or fused silica circular pieces does not exceed 40 cm, and pieces with larger dimensions have to be made to order.
It is accordingly the object of the present invention to provide an improved solar receiver window for a central solar receiver which can be made from commercially available elements.